Method and device for detecting a drop in pressure in motor vehicle tyres

ABSTRACT

The invention relates to a method for detecting a drop in pressure of a motor vehicle tire by evaluating wheel speeds determined by sensors. The method for detecting the drop in pressure is based on the detection of a large drop in pressure or a complete drop in pressure using a reduction of the angular velocity or an increase ( 8 ) in the dynamic read radius r d  of one or more wheels. The invention also relates to a device for controlling the braking power and/or driving dynamics and for measuring the pressure of vehicle tires wherein a microcomputer, which is connected to wheel rotational speed sensors and optionally to driving dynamic sensors, is used to perform the aforementioned method and a known method for regulating the braking power and/or driving dynamics.

[0001] The invention relates to a method in accordance with the preambleof claim 1 and an arrangement for determining the tire pressure inaccordance with the preamble of claim 12.

[0002] Motor vehicles, which are equipped with an electronic system forcontrolling the driving dynamic, such as ABS, ASR or ESP, usually have aunit for measuring the angular velocity of the vehicle wheels. Ameasurement of the angular velocity of the vehicle wheels can especiallytake place with the aid of active wheel rpm sensors. It is already knownthat the monitoring of a change in the angular velocity of the wheels issuitable for tire pressure loss detection.

[0003] The known systems for detecting a pressure loss practicallyalways proceed from the situation that an increase of the wheel rpm or adrop of the dynamic wheel radius results when there is a loweringpressure.

[0004] To detect the wheel rpm information, some systems store theactual wheel velocity first in a memory and evaluate this actual wheelvelocity at a later time point. Compared to systems which undertake nostorage of data, a conclusion can be drawn as to the actual drivingsituation from the trace of the wheel velocities so that fluctuations ofthe wheel angular velocities can be removed from the data which isnecessary for an adequate accuracy of the pressure loss detection. Thefluctuations of the wheel angular velocities are superposed on the tirepressure loss.

[0005] It is common for practically all known tire pressure detectionsystems that the detection system must first be advised when the desiredrated pressure P₀ of the mounted wheels is adjusted. This startingcondition for the tire pressure detection can be told to the electronicsystem, for example, by means of a reset switch which must be pressed bythe operator of the vehicle. If, after a specific time, a pressure lossoccurs at one or more wheels, the tire pressure of the affected wheeldrops by the pressure difference AP. As a consequence of the pressureloss, the dynamic rolling radius of the affected wheel changes in acharacteristic manner dependent upon the tire. As mentioned above, inknown pressure loss detection systems, a pressure loss is detected whenthe dynamic rolling radius of the affected wheel is reduced by aspecific minimum value whereby the wheel rpm increases.

[0006] Numerous methods for detecting a pressure loss have beensuggested by evaluating the wheel velocity. Known methods for detectingpressure loss on the basis of wheel rpm information often are concernedwith carrying out the pressure loss detection with still greaterreliability and accuracy. The difficulty of carrying out a pressure lossdetection with high accuracy is to distinguish a change of the dynamicrolling radius based on a pressure loss from changes of the dynamicrolling radius which can be caused, inter alia, by dynamic drivingsituations, especially driving in a curve, acceleration, deceleration,et cetera and roadway defects (potholes, various friction values) andare, as a rule, greater than the influence of a pressure loss on thedynamic rolling radius (disturbance effects).

[0007] For a pressure loss detection with high detection accuracy evenduring dynamic driving maneuvers, a method has been suggested in Germanpatent application 199 61 681. Here, additional physical data, such asyaw rate, acceleration, brake actuation, engine torque, et cetera areincluded in the detection algorithm for pressure loss detection so thata pressure loss detection can be carried out even during dynamic drivingmaneuvers (driving in a curve, acceleration, braking, et cetera).

[0008] In DE 197 21 480 A1, a pressure loss detection method isdescribed, which is integrated into an electronic anti-blocking system(ABS), wherein, after triggering the reset switch, when the ratedpressure of the wheels is adjusted, first a time limited learning phaseis run through in which a microcontroller follows wheel angularvelocities while considering the driving situation and from thetime-dependent trace of the reference values, upper and lower limitvalues (G₁ and G₂) are fixed. The reference values are formed from thewheel angular velocities. After the learning phase, a comparison phasestarts in which a check is made as to whether the actual specificreference values lie within the range defined by the learned limitvalues.

[0009] The method considers the actual driving situation by excluding,during the learning phase and during the comparison phase, referencevalues during unsuitable dynamic driving situations.

[0010] Known methods detect a pressure loss in the tire based on anincrease of the angular velocity or a drop of the dynamic rolling radiusfor one or more wheels. The quality of the detection is, however, oftennot reliable enough because the criterion for detecting is based on acomparatively small change of the wheel rpm and the wheel rpm isinfluenced by a plurality of unwanted effects to a larger extent thanthe effect to be measured.

[0011] The task of the invention is to provide a method for detecting apressure loss on the basis of the wheel rpm signals which is lesssensitive relative to unwanted effects than known methods. Such unwantedeffects are, for example, changes of the wheel rpm because of travel ina curve.

[0012] This task is solved in accordance with the invention by a methodaccording to claim 1 and an arrangement according to claim 12.

[0013] The present invention is based on the principle of detection of apressure loss based on a drop of the angular velocity or an increase ofthe dynamic rolling radius for one or more wheels.

[0014] The pressure measurement takes place in a manner known per se byevaluating angular velocities of all wheels of the vehicle or evaluatinginformations which indicate the angular velocities on the basis of timeintervals. The angular velocities are determined by sensor means.

[0015] In the detection method of the invention, the surprising effectis utilized that, when a tire has lost so much pressure that the tirerolls essentially on the emergency tread, this tire indicates anincrease of the dynamic rolling radius, that is, a detectable drop ofthe wheel velocity.

[0016] Preferably, the wheel has an emergency tread arranged within thetire casing, especially, the wheel is a run-flat wheel having anemergency tread arranged on the rim.

[0017] According to the invention, the detection of the increase of thedynamic rolling radius of a wheel can preferably take place in that:

[0018] M1: a check is made as to whether a fixed pregiven or learneddesired value is exceeded by the measured dynamic rolling radius; or,

[0019] M2: a check is made as to whether the dynamic rolling radiusincreases after it has previously dropped.

[0020] The method M2, which is especially preferred, can also be amethod combined with the methods Prog A and Prog B described below. Forexample, an initially weak drop of the dynamic rolling radius as aconsequence of a pressure loss before the tire casing seats on theemergency body (time point of the start of the flat) can be determinedfirst with the methods Prog A and Prog B. If, thereafter, the dynamicrolling radius increases sharply, then a flat is present.

[0021] In a further preferred embodiment and according to the method ofthe invention, a tire pressure loss is exclusively detected in that acheck is made that whether the angular velocity or the dynamic rollingradius of the observed wheel increases by more than a pregiven thresholdvalue.

[0022] According to the invention, suitable wheels for the vehicle are,for example, conventional tires having standard rims or preferably tireshaving emergency running characteristics, especially run-flat wheelshaving an emergency tread or run-flat tires having side walls reinforcedfor emergency running. Especially preferred are run-flat wheels havingan emergency tread which is mounted on the rim. To generate a velocitypattern, the emergency tread can be modified in a run-flat wheel orrun-flat tire in such a manner that during the rotation of the tire in aflat tire run during travel, a defined velocity pattern is generated.

[0023] A run-flat wheel which is preferably usable according to themethod of the present invention is described in DE 199 08 701.6. In thetype of tire described, the emergency tread then comes into contact withthe inner side of the tire when the tire pressure is no longer adequateto carry the load operating on the tire.

[0024] The present invention relates in a preferred embodiment also to amethod for detecting a pressure loss of tires in a motor vehicle duringtravel which is suitable for determining a comparatively slight drop ofthe tire pressure below a definable threshold value (critical tirepressure) which is carried out parallel or quasi parallel to the methoddescribed above. This further method is based on a detection known perse of a pressure loss on the basis of an increase of wheel velocity.

[0025] Preferably, additional submethods are provided which respectivelydefine a separate operational method for measuring the pressure in avehicle tire or for detecting a critical tire pressure.

[0026] The steps of the submethod or further submethods are carried outin parallel or quasi parallel in accordance with the invention. Theparallel operating submethods can be computer programs processed by amicrocomputer. If, for example, the submethods are subprograms, thenthese subprograms can be so incorporated into a main loop of anoperating program that they are called up sequentially during processingof the main loop. It is also possible that the work time of amicrocomputer, which is made available to the submethods, is subdividedbetween the individual program parts or in accordance with a time scheme“interrupt controlled”. A quasi parallel processing is understood to bewhen one of the above described procedures according to the invention ispresent.

[0027] All submethods are preferably so configured that they output asignal, for example, via a line or even via a data register, afterdetection of a pressure loss which contains the information “pressureloss”. It is understood that also additional signals, which containinformation for identifying the submethod, can be also transmitted viathis line or via a further data register.

[0028] In a preferred embodiment of the invention, a first further and asecond further submethod are carried out in parallel or quasi parallel.

[0029] The submethods generate one or more reference quantitiespreferably from the angular velocities or from information whichindicates the angular velocities on the basis of time intervals. Thevalues of the reference quantities are preferably checked as to whetherupper and lower limit values G₁, G₂ are exceeded. The second submethodespecially has limit values ^(B)G₁, ^(B)G₂ which define a narrower rangethan the limit values ^(A)G₁, ^(A)G₂ of the first submethod so that^(B)G₁<^(A)G₁ and ^(B)G₂>^(A)G₂.

[0030] Preferably, the threshold values ^(A)G₁ and ^(A)G₂ in the firstfurther submethod are so selected that a warning is outputted as to apressure loss for a residual pressure of approximately 1.0 to 1.4 bar.The threshold values ^(B)G₁ and ^(B)G₂ in the second further submethodare preferably so selected that a warning takes place in response to apressure loss already at a residual pressure of approximately 1.5 to 2.0bar.

[0031] The first further submethod responds preferably only for acomparatively large pressure loss. This submethod is therefore providedfor driving maneuvers which exhibit a high dynamic. The term “dynamicdriving maneuver” is described in the following paragraph. The secondsubmethod responds preferably already for a small pressure loss and is,because of the higher sensitivity, usable only during driving maneuvershaving a lower dynamic. The second submethod is so designed that theannouncement of the information “pressure loss” is suppressed for tightcurves or intense acceleration. In contrast, the first submethod issuitable for pressure loss detection already in non-quiet (dynamic)driving maneuvers.

[0032] Under the term “dynamic driving maneuver”, a maneuver isunderstood in the sense of the invention wherein an influence of thedriving condition on the dynamic rolling circumference or the dynamicrolling radius takes place only up to a certain minimum amount. This is,in general, then the case when low acceleration forces operate on thevehicle such as transverse acceleration Q, longitudinal acceleration Lor yaw rate ø.

[0033] The term “little dynamic driving maneuver” is understood in thesense of the invention when no dynamic driving maneuver as describedabove is present. This is preferably the case when Q is less than orequal to approximately 0.3 g, L is less than or equal to approximately0.3 g and ø is less than or equal to approximately 7°/s. If at least oneof the listed quantities lies above the above given limit values, thenpreferably a dynamic driving maneuver is present.

[0034] The two further submethods distinguish from each other especiallyin that the second submethod has a narrower limit value range than thefirst submethod. If the submethods include steps for inquiry ormonitoring of acceleration data, then, in general, the learning phaseand/or the comparison phase is interrupted when the acceleration valuesexceed fixed threshold values so that the two respective referencevalues, which are taken up in the respective method runthrough, are notconsidered.

[0035] The first submethod differs especially from the second submethodin addition in that, in the first submethod, a consideration of thespecific reference values takes place only for low dynamic drivingsituations whereas a consideration of the reference values in the secondsubmethod takes place also during dynamic driving maneuvers. This meansthat during low dynamic driving maneuvers, both submethods are activesimultaneously and during dynamic driving maneuvers, only the secondsubmethod is active.

[0036] Preferably, the second submethod is carried out only so longuntil at least an acceleration value including the longitudinalacceleration and transverse acceleration exhibits a value which is lessthan or equal to 0.15 g (here, g is the earth acceleration) or the yawrate exhibits a value of less than or equal to approximately 3°/s. Thesuppression or the switchoff of a submethod can take place in thateither the algorithm for the submethod is called up by the main programin dependence upon the driving situation or, in a submethod, a check ofthe driving conditions is undertaken.

[0037] In addition to the above described methods for pressuredetermination, a third further velocity-dependent submethod can becarried out which detects a velocity pattern of the wheel rpm trace. Thevelocity-dependent submethod detects the velocity pattern which isgenerated by a specially prepared emergency tread.

[0038] The above mentioned specially prepared emergency tread of arun-flat wheel has preferably cavities on the surface which generate acharacteristic oscillation during rolling of the emergency tread on aroadway. This oscillation is detectable based on the velocity trace ofthe wheel and is therefore measurable by means of wheel rpm sensors.

[0039] According to the invention, a first further submethod (Prog A)having a response at high pressure loss, a second further submethod(Prog B) having a response at a lower pressure loss and a third furthersubmethod (Prog S), carried out parallel or quasi parallel, is providedwhich responds when, for a vehicle tire having a specially madeemergency tread, a velocity pattern is detected which is characteristicfor a tire pressure loss.

[0040] By means of the method of the invention, it can be reliablydetected at which time point a contact occurs between emergency, treadand tire casing (flat tire). A warning announcement, which is based onthe effect of the increase of the dynamic rolling radius, iscomparatively safe and reliable because it is not a relative measurementas in conventional pressure loss detection methods. It is thereforepossible to generate additional signals or instructions proceeding fromthe occurrence of the flat tire. Accordingly, a residual runningdistance for the tire in the flat condition can be indicated.Preferably, residual running distances for the tires in the flat tirecondition are preferably indicated in accordance with the invention. Theresidual running distances can be especially dependent upon the type oftire.

[0041] Preferably, the method according to the invention is carried outto measure the pressure of the vehicle tires within a method forcontrolling the braking force and/or the driving dynamic (ABS, ASR,ESP).

[0042] The outputs of the submethods, which contain information as to apressure loss, are preferably OR-coupled to a common output. This outputcan, for example, be connected to a warning lamp in the dashboard.

[0043] The method of the invention requires only units which are anywaypresent in a conventionally used ABS, ASR or ESP system. For thisreason, this method can be cost-effectively integrated into such asystem in an advantageous manner.

[0044] The intention therefore relates also to an arrangement forcontrolling the braking force and/or the driving dynamic and formeasuring the pressure of vehicle tires which is characterized in that amicrocomputer processes an above-described method according to theinvention and a method known per se for controlling the braking forceand/or driving dynamic. The microcomputer is connected to wheel rpmsensors and, if needed, additional driving dynamic sensors.

[0045] In the following, the method of the invention is explained ingreater detail with respect to an embodiment and the figures.

[0046]FIG. 1 shows a schematic representation of a method for pressureloss detection having several submethods;

[0047]FIG. 2a shows a diagram having a time-dependent trace of areference value formed from the wheel signals;

[0048]FIG. 2b shows a further diagram having a time-dependent trace of areference value, which is formed from the wheel signals, plus limitvalues for the pressure determination in accordance with the methodknown per se;

[0049]FIG. 3 is a diagram having the trace of the dynamic wheel radiusr_(d) in dependence upon the tire pressure P; and,

[0050]FIG. 4 is a schematic view of a section of a run-flat wheel havingan emergency tread on the rim.

[0051] In FIG. 1, an example is shown for a preferred method accordingto the invention having three or four quasi parallel configuredsubmethods Prog A, Prog B, Prog V and/or Prog S. The present inventionrelates especially to the submethod “Prog V”.

[0052] With a connection “reset”, the submethods in FIG. 1 can be resetto their starting state. Line “input” symbolizes the connection for thesignals of the four wheel rpm sensors of the motor vehicle. Thesubmethods have outputs 2 which are combined via a coupling element ORto a common output signal 3. The coupling element OR is an OR coupling.The output signal 3 can be connected to a warning lamp 4.

[0053] The unit 1, which is shown in FIG. 1, includes the submethods“Prog A” and “Prog B”. With unit 1 and according to the basic principle,the known pressure loss detection can be carried out for all tire types(standard tires, run-flat wheels). The submethods (Prog V, Prog S) areespecially suitable for special tires, such as tires having a generatingdevice for a velocity pattern or tires having an emergency tread.

[0054] Submethod “Prog V” functions to detect a velocity pattern in thewheel rpm trace. Submethod “Prog S” functions to detect an increase ofthe dynamic wheel radius. As with the submethods “Prog A” and “Prog B”,both submethods (Prog V, Prog S) define separately operational methodsfor detecting a pressure loss in tires of a motor vehicle. The submethod“Prog S” and “Prog V” are comparatively less sensitive with respect todynamic driving situations.

[0055] As described in greater detail below and as shown in FIG. 2b, thesubmethod “Prog A” can be so configured that coarse thresholds are fixedby values ^(A)G₁ and ^(A)G² during the learning phase so that an end ofthe learning phase can take place comparatively fast after the reset bypressing the reset key when filling the tires to the initial ratedpressure. Even when, after filling the tire, one drives exclusively sothat the vehicle is for a long time in a dynamic driving state, thelearning method can already be ended after a time of preferably lessthan approximately one minute.

Description of the Method Steps of Prog V (Method According to theInvention

[0056] The operation of Prog V is explained in greater detail withrespect to FIGS. 3 and 4. If run-flat wheels 9 are mounted on the motorvehicle, then the dynamic rolling radius r_(d) first drops in dependenceupon tire pressure as in a conventional tire (reference numeral 7). Ifthe pressure loss is so great that the emergency tread 10, which isprovided in a run-flat wheel, touches the casing 11 of the tire, thenthe dynamic rolling radius increases greatly (reference numeral 8).

[0057] The method “Prog V” conducts a check as to a drop of therotational velocity of the wheels which is a consequence of the increaseof the dynamic rolling radius r_(d).

[0058] The method for detection in method “Prog V” by means of velocitychanges of the wheels, can, in specific tire types, be considerably lesssensitive than in the methods “Prog A” and “Prog B” described in detainhereinafter. In this method, it is already sufficient to monitor theindividual wheel velocities or reciprocal wheel velocities (time values)directly as to exceeding (dropping below) fixed pregiven limit valueswhich are dependent upon the type of tire used. Practically, these limitvalues need not be learned in the system in a learning method asdescribed hereinafter; rather, it is possible to store fixedly storedtire-type dependent limit values in a data bank.

Description of the Method Steps of Prog A (First Further Submethod)

[0059] Step A1:

[0060] Picking up the angular velocities by means of wheel sensors ofthe wheels w₁, W₂, W₃ and W₄; wherein: w₁ identifies the right forwardwheel, w₂ the left forward wheel, W₃ the right rear wheel and w₄ theleft rear wheel. Instead of a value for the angular velocity w, atime-dependent quantity T can preferably be used as an index for thewheel velocity, especially, a synchronization to a sensor flank can takeplace. This affords the advantage of increased accuracy in thedetermination of the wheel velocities.

[0061] Step A2:

[0062] Determining comparison values (learning phase) via the steps A2ato A2g.

[0063] Step A2a:

[0064] Forming reference values in accordance with the equation

Ref_(i)=(w _(k) +w ₁)/(w _(m) +w _(n))

[0065] from current values of w (or, preferably a time T), with thevalues being determined in accordance with the method under point 1;wherein i=1 . . . 3 and the w_(i) identify different wheels with eachreference value.

[0066] In FIGS. 2a and 2 b, an example is shown for a trace ofRef₁=(w_(k)+w₁)/(w_(m)+w_(n)) in dependence upon the time t; wherein:k=forward left, l=rearward right, m=forward right and n=rearward left.The trace of curve 5 or 6 provides information as to deviations of thedynamic rolling radius for a pressure loss. If all wheels would have thesame angular velocity for ideal conditions, then the value of thereference value would be Ref₁=1. For a pressure loss, the referencevalue deviates by a specific amount from the value 1. The trace of Ref₁is, however, dependent by a significantly greater amount on the actualdriving conditions such as roadway characteristics, acceleration ordriving in a curve.

[0067] Step A2b:

[0068] Checking whether the driving conditions or driving situation liesin a permissible range. If a driving condition is present which does notappear to be purposeful for forming the reference values (for example,when the longitudinal acceleration, the transverse acceleration or thewheel acceleration exceed specific threshold values), then the submethodis not carried out.

[0069] Step A2c:

[0070] Generating filtered reference values {overscore (Ref)}_(i), forexample, by means of a lowpass filter of the first order. The lowpassfiltering can be carried out either by evaluating stored data ofreference values or by means of a recursion method for lowpassfiltering.

[0071] Step A2d:

[0072] Storing upper and lower limits of the filtered and unfilteredreference values _(i)Ref^(Max) and _(l)Ref^(Min) and generating a meanvalue Ref^(M) from the earlier data or recursive generation of a meanvalue.

[0073] Step A2e:

[0074] Repeat steps A1 to A2d until the number of determined referencevalues has reached a value N (N>1, preferably N>5) and check as towhether the difference of _(i)Ref^(Max) and _(i)Ref^(Min) does notexceed a specific threshold value. If this threshold value is exceeded,then the submethod is begun anew.

[0075] Step A2f:

[0076] Storing upper and lower limit values _(l)G₁, _(i)G₂ in dependenceupon the reference values which are determined in the elapsed time span(learn phase); wherein an offset value is added to or subtracted fromthe mean value Ref^(M) for forming the limit values.

[0077] Step A2q:

[0078] Continuing the execution of the program in the program part“comparison phase” which is described under point 3.

Description of the Method Steps of Prog B (Second Further Submethod)

[0079] Compared to the method described under point 2, the method stepsof Prog A are modified in Prog B in a manner described hereinafter. Themethod described here corresponds substantially to the method presentedin DE 197 21 480 A1 for the description of FIG. 2. In this method, acurrent sample is compared to a sample stored at an earlier time point.The method “Prog B” has a considerably higher time requirement comparedto Prog A. For this reason, the method “Prog B” can lead to a successfuldetermination of comparison values when the method of Prog A under point2 is not suitable to determine comparison values based on a dynamicdriving situation.

[0080] Step B1:

[0081] Picking up the wheel rpm signals of the individual wheels. Here,a check can be made as to whether no driving condition is present whichmakes it appear not purposeful to form the reference values. When it isdetected that such a driving condition is present, the currentrunthrough of the method is ended. Otherwise, a transition to step B2takes place.

[0082] Step B2:

[0083] From the measured wheel rpms, at least one reference value of thereference values Ref₁, Ref₂, Ref₃ is formed as described above. Heretoo, as likewise described above, a formation of the reference valuescan take place either via time signals T or by utilizing wheelvelocities.

[0084] Step B3:

[0085] Generating an additional set of data from the determinedreference values by lowpass filtering. Here too, the lowpass filteringcan be a recursive method which stores only the last filtered value at acurrent time point.

[0086] Step B4:

[0087] Check whether the currently determined filtered reference valueis greater than the maximum value of the unfiltered reference valuesdetermined up to now and, if required, storing the new maximum value. Inthe same manner, the instantaneously valid minimal value is alsodetermined. Additionally, it can be practical to also continuouslydetermine a mean value from the unfiltered reference values as well asto determine the standard deviation corresponding thereto.

[0088] Step B5:

[0089] Checking whether a further pregiven number N of reference valueswas determined, that is, whether a complete sample of reference valueswas recorded. If this is not the case, then the current runthrough ofthe method is ended. Otherwise, the method is continued.

[0090] Step B6:

[0091] Checking whether the maximum value of the filtered referencevalues of the current recorded sample deviates by no more than apregiven amount from the maximum value of the filtered reference valueof the last stored sample. Furthermore, a check is made in this stepwhether the minimum value of the described reference values of thecurrent recorded sample deviates by no more than a pregiven amount fromthe minimum value of the described reference values of the last storedsample. Otherwise, the method is repeated until the condition issatisfied.

[0092] Step B7:

[0093] If required, checking whether the mean value of the unfilteredreference values of the current sample deviates by no more than aspecific amount from the mean value of the unfiltered reference valuesof the last stored sample. Furthermore, a check takes place, whenpractical, as to whether the mean value of the unfiltered referencevalues of the current sample plus as well as minus a multiple of aquality index lies within the limits which are given by the upper limitvalue and the lower limit value. This multiple can, for example, amountto the fourfold. Otherwise, the method is ended.

[0094] Step B8:

[0095] Determination of an upper limit value in that an offset value isadded to the maximum value of the filtered reference values of thecurrent sample. A lower limit value is determined in that an offsetvalue is subtracted from the minimum value of the filtered referencevalues of the current sample.

[0096] If one of the checks yielded the result that the deviations ofthe values in the current sample were too large, then a transition takesplace to step B6 in that the corresponding values of the current sample(mean value, standard deviation of the unfiltered reference values,maximum value and minimum value of the filtered reference values of thecurrent sample) are stored for comparison to future recorded samples.

[0097] 3) Comparison Phase

[0098] Determination of reference values in accordance with point 2a orB2 and computation in accordance with one of the formulas: (Formula A)_(i)G₁ < _(i)Ref < _(i)G₂ or (Formula B) _(i)G₁ < _(i)Ref^(Filt) < ₁G₂,

[0099] wherein _(i)Ref^(Filt) can be reference values filtered in amanner known per se. With the computation according to one of theformulas A or B, a check can be made in accordance with the method ofthe invention as to whether a pressure loss has occurred. If a pressureloss is present, then information as to the pressure loss of the wheelis outputted. If several reference values are formed, that wheel can beindividually identified which exhibits the pressure loss from aconsideration of the reference values in a practical manner.

Description of the Method Steps of Prog S (Third Further Submethod)

[0100] The method “Prog S” functions to detect a velocity pattern of aspecial-wheel/tire suitable for generating a velocity pattern. A methodusable in accordance with the invention is described in the publicationDE 199 08 701.6 mentioned initially herein. The wheel can be equippedwith an emergency tread which is modified for generating the velocitypattern.

[0101] Also with this method, the wheel rpm signals of the wheels aredetected by the ABS system and are transmitted to the central computerunit. The periodic oscillation, which is proportional to the wheel rpmand characteristic for the emergency state, is generated by an emergencybody 10 supported on the rim 12. On its emergency tread 13, theemergency body has a plurality of indentations which are uniformly ornon-uniformly distributed over the periphery.

[0102] According to the method, the wheel velocities are first recordedwithin defined count times. With the aid of the indentations, periodicoscillations of the n-th order of the tire period (for example, n=13)are generated. These oscillations are proportional to the wheel rpm andare characteristically defined separately. If these oscillations arereferred to the mean value of the wheel rpm, then zero crossover timesof the rpm output signal can be given. For a conventional tire, thedistances of the zero crossover times are essentially constant; whereas,for the special tire used here, significant noticeable periodicdeviations of approximately 0.02 milliseconds result.

[0103] According to the method given in this example, the set of datafrom the zero crossover times in dependence upon the time is analyzedvia numerical Fourier transformation (FFT). In this way, a spectralpower density is obtained plotted as a function of the frequency.

[0104] Peaks can be reliably determined based on the data curve havingthe spectral power density as a function of the frequency with the datacurve being obtained in accordance with the transformation. These peaksare caused by the velocity variation of the special tire. To evaluatethese signals, specific pregiven frequency ranges of the transformedsignals are then integrated. Thereafter, the determined integral valuesare compared to reference values and/or threshold values and, when apregiven difference to the reference and/or threshold values isexceeded, a warning signal is outputted to a warning device mounted inthe field of view of the driver.

[0105] The threshold value, which is used with the method “Prog V” mustbe selected so large that an increase of the wheel velocities can bereliably excluded, for example, via sun radiation on a tire. Suitablevalues are determined by the technician from driving experiments. Thevalues are dependent in a sensitive manner from the tire and vehicletype.

1. Method for detecting a pressure loss of tires in a motor vehicleduring travel, especially for detecting the seating of the tire casingon an emergency tread present in the tire or the lowering of the tirepressure below a threshold value (critical tire pressure), viaevaluation of sensor determined angular velocities of the wheels of themotor vehicle or evaluation of informations, which indicate the angularvelocities on the basis of time intervals, characterized in that themethod for pressure loss detection is based on detecting a high pressureloss or a total pressure loss based on a reduction of the angularvelocity and/or of an increase of the dynamic rolling radius r_(d) inone or more wheels.
 2. Method of claim 1, characterized in that apressure loss is detected: (M1) when the current value of the angularvelocity or of the dynamic rolling radius has increased relative to aninitial value of the considered wheel or a fixed pregiven thresholdvalue, the initial value being stored at an earlier time point; or, (M2)in that a check is made as to whether the dynamic rolling radiusincreases after this rolling radius has dropped off previously as aconsequence of a pressure loss detectable in a manner known per se. 3.Method of claim 1 or 2, characterized in that the motor vehicle wheelsare run-flat wheels having an emergency tread mounted on the rim orwithin the tire casing.
 4. Method of at least one of the claims 1 to 3,characterized in that the pressure determining method includesadditionally further submethods which detect pressure losses of lesseramount based on a drop of the angular velocity or of the dynamic rollingradius; and, the steps of the submethod are carried out in parallel orquasi parallel.
 5. Method of claim 4, characterized in that the pressureloss detecting method includes a first further submethod (Prog A) and asecond further submethod (Prog B); both further submethods generate oneor more reference quantities Refi from the angular velocities orinformations which indicate the angular velocities on the basis of timeintervals; and, thereupon checking the reference quantity or quantitiesas to whether upper and lower limit values G₁ and G₂ are exceeded; and,the second further submethod (Prog B) has limit values ^(B)G₁ and ^(B)G₂which define a narrower range than the limit values ^(A)G₁ and ^(A)G₂ ofthe first further submethod (Prog A) so that ^(B)G₁<^(A)G₁ and^(B)G₂>^(A)G₂.
 6. Method of at least one of the claims 1 to 5,characterized in that at least one of the submethods is a third furthersubmethod (Prog S) which detects a velocity pattern of the wheel rpmtrace which is generated by a vehicle tire having a specially providedemergency tread.
 7. Method of claim 6, characterized in that thespecially provided emergency tread has cavities on the surface which,during rolling of the emergency tread on a roadway, generate anoscillation which is characteristic for the emergency state and isdetectable by means of wheel rpm sensors.
 8. Method of at least one ofthe claims 1 to 7, characterized in that the following are provided: afirst submethod (Prog A) having a response at a high pressure loss, asecond submethod (Prog B) having a response at a lower pressure loss anda third parallel or quasi parallel executed submethod (Prog S) whichresponds when a velocity pattern is detected for a vehicle tire having aspecially provided emergency tread and which velocity pattern ischaracteristic for a tire pressure loss.
 9. Method of at least one ofthe claims 1 to 8, characterized in that the method for measuring thepressure of vehicle tires is carried out within a method for the controlof the braking force and/or of the driving dynamic (ABS, ASR, ESP). 10.Method of at least one of the claims 1 to 9, characterized in that thereference quantity Ref₁ is formed in that the sums of each two signals,which represent the wheel rpms, are divided.
 11. Method of at least oneof the claims 1 to 10, characterized in that the outputs of thesubmethods are OR coupled to a common output with the outputs containinginformation as to a pressure loss.
 12. Arrangement for controlling thebraking force and/or the driving dynamic and for measuring the pressureof tires in a motor vehicle, characterized in that a microcomputer,which is connected to wheel rpm sensors and, if required, additionallyto driving dynamic sensors, processes a method of the claims 1 to 11 anda method known per se for the control of the braking force and/ordriving dynamic.